Ltps array substrate and method for producing the same

ABSTRACT

An LTPS array substrate and a method for producing the same are proposed. The method includes: forming an insulating layer, a semiconductor layer, and a first positive photoresist layer on the substrate one by one; exposing one side of the substrate on the opposite side of the gate for forming a polycrystalline silicon layer; forming a source and a drain of the TFT on the polycrystalline silicon layer; forming a pixel electrode on the insulating layer and part of the source; forming a plain passivation layer on a source-drain electrode layer; forming a transparent electrode layer on the plain passivation layer so that the transparent electrode layer is connected to the gate, the source, and the drain via the contact hole. The use of masks in types and in numbers in the LTPS technology will be reduced. So, both of the processes and the production costs are reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of display technology, and more particularly, to a low temperature poly-silicon (LTPS) array substrate and a method for producing the LTPS array substrate.

2. Description of the Prior Art

Higher electron mobility is demonstrated in a liquid crystal display (LCD) adopting LTPS. The size of a thin film transistor (TFT) is actually smaller in this kind of LCD in which the aperture rate of a pixel is higher, and the brightness is larger. Anyway, power consumption and production costs are less using an LCD withLTPS. Owing to these features, the research on the LCD with LTPS is popular in LCD technology. However, the LTPS technology is sophisticated. It requires a lot of masks in various types to fabricate an array substrate (array substrate). Also, it needs many processes to produce an array substrate. Therefore, production costs are always high, which is a problem. To find ways to reduce the masks used in the LTPS technology in numbers and types requires the whole industry to work out.

SUMMARY OF THE INVENTION

In view of this, an LTPS array substrate and a method for producing the LTPS array substrate is proposed by the embodiment of the present invention for the purpose of reducing the masks used in the LTPS technology in types and in numbers.

According to a preferred embodiment of the present invention, a method for producing a low temperature poly-silicon (LTPS) array substrate comprises: forming a gate of a thin-film transistor (TFT) of the LTPS array substrate on a substrate; forming a buffer layer on the substrate without being covered by the gate and forming a plane using an upper surface of the buffer layer and an upper surface of the gate; forming an insulating layer, a semiconductor layer, and a first positive photoresist layer on the substrate one by one in which an upper surface of the insulating layer is a plane; exposing one side of the substrate on an opposite of the gate for only preserving the first positive photoresist layer disposed on a first section disposed right above the gate; injecting first impurity ions into the semiconductor layer outside the first section; exposing one side of the substrate on the opposite side of the gate for forming the first positive photoresist layer disposed on a second section disposed right above the gate, and the second section being smaller than the first section; injecting second impurity ions into the semiconductor layer outside the second section; removing the first positive photoresist layer disposed on the second section to form a polycrystalline silicon layer; forming a source and a drain of the TFT on the polycrystalline silicon layer; forming a pixel electrode on the insulating layer and part of the source; forming a plain passivation layer on a source-drain electrode layer, which is fabricated from the source and the drain, and forming a contact via in the plain passivation layer for exposing surfaces of the gate, the source, and the drain, and the contact via being disposed outside the polycrystalline silicon layer; forming a transparent electrode layer on the plain passivation layer so that the transparent electrode layer can be electrically connected to the gate, the source, and the drain via the contact hole.

Furthermore, a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a negative photoresist layer on the substrate one by one; exposing one side of the substrate on the opposite side of the gate for removing the negative photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.

Furthermore, a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a second positive photoresist layer on the substrate one by one; exposing one side of the substrate facing the gate for removing the second positive photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.

Furthermore, after removing the first positive photoresist layer on the second section, the method further comprises: coating a photoresist layer on the polycrystalline silicon layer and exposing the photoresist layer based on a desired pattern; etching the polycrystalline silicon layer without the desired pattern; removing the remaining photoresist layer.

Furthermore, the first impurity ions are N+ type impurity ions, and the second impurity ions are N− type impurity ions.

According to another embodiment of the present invention, a method for producing a low temperature poly-silicon (LTPS) array substrate, comprises: forming a gate of a thin-film transistor (TFT) of the LTPS array substrate on a substrate; forming an insulating layer, a semiconductor layer, and a first positive photoresist layer on the substrate one by one in which an upper surface of the insulating layer is a plane; exposing one side of the substrate on the opposite side of the gate for forming a polycrystalline silicon layer; forming a source and a drain of the TFT on the polycrystalline silicon layer; forming a pixel electrode on the insulating layer and part of the source; forming a plain passivation layer on a source-drain electrode layer, which is fabricated from the source and the drain, and forming a contact via in the plain passivation layer for exposing surfaces of the gate, the source, and the drain, and the contact via being disposed outside the polycrystalline silicon layer; forming a transparent electrode layer on the plain passivation layer so that the transparent electrode layer can be electrically connected to the gate, the source, and the drain via the contact hole.

Furthermore, before the insulating layer is formed on the substrate of the gate, the method further comprises: forming a buffer layer on the substrate without being covered by the gate and forming a plane using an upper surface of the buffer layer and an upper surface of the gate.

Furthermore, a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a negative photoresist layer on the substrate one by one; exposing one side of the substrate on the opposite side of the gate for removing the negative photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.

Furthermore, a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a second positive photoresist layer on the substrate one by one; exposing one side of the substrate facing the gate for removing the second positive photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.

Furthermore, a step of exposing one side of the substrate on the opposite side of the gate for forming a polycrystalline silicon layer comprises: exposing one side of the substrate on the opposite of the gate for only preserving the first positive photoresist layer disposed on a first section disposed right above the gate; injecting first impurity ions into the semiconductor layer outside the first section; exposing one side of the substrate on the opposite side of the gate for forming the first positive photoresist layer disposed on a second section disposed right above the gate, and the second section being smaller than the first section; injecting second impurity ions into the semiconductor layer outside the second section; removing the first positive photoresist layer disposed on the second section.

Furthermore, after removing the first positive photoresist layer on the second section, the method further comprises: coating a photoresist layer on the polycrystalline silicon layer and exposing the photoresist layer based on a desired pattern; etching the polycrystalline silicon layer without the desired pattern; removing the remaining photoresist layer.

Furthermore, the first impurity ions are N+ type impurity ions, and the second impurity ions are N− type impurity ions.

Furthermore, steps of exposing one side of the substrate on the opposite side of the gate for forming the polycrystalline silicon layer comprise: exposing one side of the substrate on the opposite side of the gate for only preserving the first positive photoresist layer disposed on a first section disposed right above the gate; injecting P-type impurity ions into the semiconductor layer outside the first section; exposing one side of the substrate on the opposite side of the gate for forming the first positive photoresist layer disposed on a second section disposed right above the gate, and the second section being smaller than the first section; removing the first positive photoresist layer disposed on the second section.

According to another embodiment of the present invention, a low temperature poly-silicon (LTPS) array substrate, comprises: a substrate; a gate, disposed on the substrate; forming an insulating layer and a polycrystalline silicon layer on the substrate one by one in which an upper surface of the insulating layer is a plane; a source and a drain, disposed on the polycrystalline silicon layer; a pixel electrode, disposed on the insulating layer and part of the source; a plain passivation layer, disposed on a source-drain electrode layer fabricated from the source and the drain, and a contact via formed in the plain passivation layer for exposing surfaces of the gate, the source, and the drain, the contact via disposed outside the polycrystalline silicon layer; a transparent electrode layer, disposed on the plain passivation layer, and the transparent electrode layer being electrically connected to the gate, the source, and the drain via the contact hole.

Furthermore, the LTPS array substrate further comprises a buffer layer, the buffer layer is disposed on the substrate without being covered by the gate, and an upper surface of the buffer layer and an upper surface of the gate form a plane.

The fact about the LTPS array substrate and the method for producing the LTPS array substrate proposed by the present invention is that one side of a substrate on the opposite side of a gate is exposed for forming a polycrystalline silicon layer. In other words, an opaque gate is exposed for forming a polycrystalline silicon layer. It is unnecessary to use any masks in producing polycrystalline silicon layers so the use of masks in types and in numbers in the LTPS technology will be reduced. So, both of the processes and the production costs are reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method for producing an LTPS array substrate according to a preferred embodiment of the present invention.

FIG. 2 shows a process of forming a gate according to the present invention.

FIG. 3 shows a process of forming an insulating layer, a semiconductor layer, and a positive photoresist formed on the substrate according to the present invention.

FIG. 4 shows a process of forming a polycrystalline silicon layer according to the present invention.

FIG. 5 shows a patterned polycrystalline silicon layer according to the present invention.

FIG. 6 shows a process of forming a source and a drain according to the present invention.

FIG. 7 shows a process of forming a pixel electrode according to the present invention.

FIG. 8 shows a first cross-sectional view of forming a transparent electrode according to the present invention.

FIG. 9 shows a process of forming a passivation layer according to the present invention.

FIG. 10 shows a second cross-sectional view of forming a transparent electrode according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a flow chart of a method for producing an LTPS array substrate according to a preferred embodiment of the present invention. The method comprises following steps of:

Step 11: Forming a gate of a thin-film transistor (TFT) of the LTPS array substrate on a substrate.

Please refer to FIG. 2. The substrate 21 is used for forming the LTPS array substrate of the LCD panel. The substrate 21 can be a glass substrate, a plastic substrate, or a flexible substrate.

A first metallic layer is formed on the substrate 21 and the first metallic layer is exposed through a first mask in this embodiment. The exposed first metallic layer is patterned after being developed and etched. Then, a gate 22 is formed. The first metallic layer is etched with etching liquid comprising phosphoric acid, nitric acid, acetic acid, and deionized water. Definitely, the first metallic layer can undergo dry etching as well.

The gate 22 can be acquired through other methods as well such as chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), sputtering, vacuum evaporation deposition, or low pressure chemical vapor deposition (LP-CVD). The method of deposition is not confined in the specification. The gate 22 with a desired pattern is formed on the substrate 21 directly. The first metallic layer is fabricated from metal such as aluminum (AL), molybdenum (Mo), titanium (Ti), chromium (Cr), or cuprum (Cu). Or, the first metallic layer is fabricated from metallic oxide, such as titanium oxide, or metallic alloy or other conducting materials.

Step 12: Forming an insulating layer, a semiconductor layer, and a positive photoresist layer on the substrate one by one in which the upper surface of the insulating layer is a plane.

Please refer to FIG. 3 as well. A buffer layer 23 needs to be formed on the substrate 21 without being covered by the gate 22 before the insulating layer 25, the semiconductor layer 26, and the positive photoresist layer 27 are formed in this embodiment. The concrete processes are described below while it does not mean that the processes are limited.

Firstly, the buffer layer 23 and a negative photoresist layer 24 are formed on the substrate 21 of the gate 22 one by one. The buffer layer 23 can be a SiN_(x) layer, a SiO_(x) layer or the combination of other non-conducting materials. The buffer layer 23 is used for preventing upward spreading of the impurity in the substrate 21 in the following processes so that the quality of a LTPS layer which will be formed in the following processes will not be affected. The SiN_(x) layer and the SiO_(x) layer are deposited through CVD, PECVD, sputtering, vacuum evaporation deposition, or LP-CVD. The method of deposition is not confined in the specification.

Next, one side of the substrate 21 on the opposite side of the gate 22 is exposed. The negative photoresist layer 24 disposed right above the gate 22 is not exposed under the shelter of the gate 22 so the negative photoresist layer 24 can be removed with ash after being developed.

Finally, the remaining negative photoresist layer 24 is lifted off. The buffer layer 23 disposed right above the gate 22 is etched and removed. Therefore, the buffer layer 23 without being covered by the gate 22 is preserved.

The present embodiment further proposes a method for forming the buffer layer 23. It is as follows:

Firstly, the buffer layer 23, the positive photoresist layer, the positive photoresist layer 27 relatively formed on the semiconductor layer 26 are formed on the substrate 21 of the gate 22 one by one. The positive photoresist layer can be understood as the second positive photoresist layer. The positive photoresist layer 27 is the first positive photoresist layer. Then, one side of the substrate 21 facing the gate 22 is exposed to remove the positive photoresist layer disposed right above the gate 22. Finally, the buffer layer 23 disposed right above the substrate 21 is removed. The buffer layer 23 on the substrate without being covered by the gate 22 is preserved.

Step 13: Exposing one side of the substrate on the opposite side of the gate for forming a polycrystalline silicon layer.

Please refer to FIG. 4 as well. Firstly, one side of the substrate 21 on the opposite side of the gate 22 is exposed. The positive photoresist layer 27 disposed on the first section Q₁ of the gate 22 is not exposed under the shelter of the gate 22 so the positive photoresist layer 27 is preserved after being developed. The positive photoresist layer 27 without being exposed under the shelter of the gate 22 can be removed with ash after being developed. Therefore, only the positive photoresist layer 27 disposed on the first section Q₁ disposed right above the gate 22 is preserved.

Next, first impurity ions are injected into the semiconductor layer 26 outside the first section Q₁. In other words, conventionally, the semiconductor layer 26 is heavily doped.

Next, one side of the substrate 21 on the opposite side of the gate 22 is exposed. The intensity of this exposure is larger than the intensity of exposure on the positive photoresist layer 27 formed on the first section Q₁. So the positive photoresist layer 27 disposed on both sides of the first section Q₁ is removed. The positive photoresist layer 27 of the second section Q₂ is formed right above the gate 22. The second section Q₂ is smaller than the first section Q₁.

Further, second impurity ions are injected into the semiconductor layer 26 outside the second section Q₂. In other words, conventionally, the semiconductor layer 26 is softly doped.

Finally, the positive photoresist layer 27 on the second section Q₂ is removed. The first impurity ions in this embodiment can be N+ type impurity ions, and correspondingly, the second impurity ions can be N− type impurity ions. While the first impurity ions are P+ type impurity ions, the doping of the second impurity ion is unnecessary. In other words, soft doping is unnecessary.

After the positive photoresist layer 27 is removed from the second section Q₂, a polycrystalline silicon layer 28 is exposed through a second mask for forming a desired pattern on the polycrystalline silicon layer 28. Please refer to FIG. 5 as well. A photoresist layer 29 is coated on the polycrystalline silicon layer 28 and exposed. Then, the polycrystalline silicon layer 28 where no desired pattern is formed is etched and removed. Meanwhile, the remaining photoresist layer 29 is removed as well. One side of the substrate 21 on the opposite side of the gate 22 is exposed when the photoresist layer 29 is a positive photoresist layer. One side of the substrate 21 facing the gate 22 is exposed when the photoresist layer 29 is a negative photoresist layer.

Step S14: Forming a source and a drain of the TFT on the polycrystalline silicon layer.

Asource S and a drain D of the TFTare formed through exposure, development, and etching through a third mask in this embodiment, as shown in FIG. 6.

Step S15: Forming a pixel electrode on the insulating layer and part of the source.

Apixel electrode 30 with a desired pattern is formed through exposure, development, and etching through a fourth mask in this embodiment, as shown in FIG. 7.

Step S16: Forming a plain passivation layer on a source-drain electrode layer, which is fabricated from the source and the drain, and forming a contact via in the plain passivation layer for exposing the surfaces of the gate, the source, and the drain; the contact via being disposed outside the polycrystalline silicon layer.

Step S17: Forming a transparent electrode layer on the plain passivation layer so that the transparent electrode layer can be electrically connected to the gate, the source, and the drain via the contact hole.

The plain passivation layer 31 is formed through exposure, development, and etching through a fifth mask in this embodiment, as shown in FIG. 8 and FIG. 9. Please refer to FIG. 8. Outside the TFT, the plain passivation layer 31 comprises a contact via O. Because of the contact via O, the surfaces of the gate 22, the source S, and the drain D are exposed and electrically connected to wires of the LTPS array substrate. For example, the gate 22 is correspondingly electrically connected to a gate wire formed on the substrate 21 (array substrate). The source S is correspondingly electrically connected to a data wire formed on the array substrate. The gate wire and the data wire are vertically crossed and form a pixel display section where the pixel electrode 33 is disposed.

A transparent electrode layer 32 is formed through exposure, development, and etching through a sixth mask in this embodiment, as shown in FIG. 10. The transparent electrode layer 32 and the pixel electrode 30 are fabricated from the same transparent conducting materials and used as a common electrode of the LTPS array substrate.

One side of the substrate 21 on the opposite side of the gate 22 is exposed. In other words, the opaque gate 22 is exposed for forming the polycrystalline silicon layer 28 without using any masks. Therefore, the type and number of masks for producing the LTPS array panel is reduced. It not only simplifies the manufacture procedure but also reduces costs.

The present invention further proposes an LCD panel comprising the LTPS array panel as shown in FIG. 10 and an LCD. The benefit is as what is described above.

The present disclosure is described in detail in accordance with the above contents with the specific preferred examples. However, this present disclosure is not limited to the specific examples. For the ordinary technical personnel of the technical field of the present disclosure, on the premise of keeping the conception of the present disclosure, the technical personnel can also make simple deductions or replacements, and all of which should be considered to belong to the protection scope of the present disclosure. 

What is claimed is:
 1. A method for producing a low temperature poly-silicon (LTPS) array substrate, comprising: forming a gate of a thin-film transistor (TFT) of the LTPS array substrate on a substrate; forming a buffer layer on the substrate without being covered by the gate and forming a plane using an upper surface of the buffer layer and an upper surface of the gate; forming an insulating layer, a semiconductor layer, and a first positive photoresist layer on the substrate one by one in which an upper surface of the insulating layer is a plane; exposing one side of the substrate on an opposite of the gate for only preserving the first positive photoresist layer disposed on a first section disposed right above the gate; injecting first impurity ions into the semiconductor layer outside the first section; exposing one side of the substrate on the opposite side of the gate for forming the first positive photoresist layer disposed on a second section disposed right above the gate, and the second section being smaller than the first section; injecting second impurity ions into the semiconductor layer outside the second section; removing the first positive photoresist layer disposed on the second section to form a polycrystalline silicon layer; forming a source and a drain of the TFT on the polycrystalline silicon layer; forming a pixel electrode on the insulating layer and part of the source; forming a plain passivation layer on a source-drain electrode layer, which is fabricated from the source and the drain, and forming a contact via in the plain passivation layer for exposing surfaces of the gate, the source, and the drain, and the contact via being disposed outside the polycrystalline silicon layer; forming a transparent electrode layer on the plain passivation layer so that the transparent electrode layer can be electrically connected to the gate, the source, and the drain via the contact hole.
 2. The method of claim 1, wherein a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a negative photoresist layer on the substrate one by one; exposing one side of the substrate on the opposite side of the gate for removing the negative photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.
 3. The method of claim 1, wherein a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a second positive photoresist layer on the substrate one by one; exposing one side of the substrate facing the gate for removing the second positive photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.
 4. The method of claim 1, wherein after removing the first positive photoresist layer on the second section, the method further comprises: coating a photoresist layer on the polycrystalline silicon layer and exposing the photoresist layer based on a desired pattern; etching the polycrystalline silicon layer without the desired pattern; removing the remaining photoresist layer.
 5. The method of claim 1, wherein the first impurity ions are N+ type impurity ions, and the second impurity ions are N− type impurity ions.
 6. A method for producing a low temperature poly-silicon (LTPS) array substrate, comprising: forming a gate of a thin-film transistor (TFT) of the LTPS array substrate on a substrate; forming an insulating layer, a semiconductor layer, and a first positive photoresist layer on the substrate one by one in which an upper surface of the insulating layer is a plane; exposing one side of the substrate on the opposite side of the gate for forming a polycrystalline silicon layer; forming a source and a drain of the TFT on the polycrystalline silicon layer; forming a pixel electrode on the insulating layer and part of the source; forming a plain passivation layer on a source-drain electrode layer, which is fabricated from the source and the drain, and forming a contact via in the plain passivation layer for exposing surfaces of the gate, the source, and the drain, and the contact via being disposed outside the polycrystalline silicon layer; forming a transparent electrode layer on the plain passivation layer so that the transparent electrode layer can be electrically connected to the gate, the source, and the drain via the contact hole.
 7. The method of claim 6, wherein before the insulating layer is formed on the substrate of the gate, the method further comprises: forming a buffer layer on the substrate without being covered by the gate and forming a plane using an upper surface of the buffer layer and an upper surface of the gate.
 8. The method of claim 7, wherein a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a negative photoresist layer on the substrate one by one; exposing one side of the substrate on the opposite side of the gate for removing the negative photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.
 9. The method of claim 7, wherein a step of forming the buffer layer on the substrate without being covered by the gate comprises: forming the buffer layer and a second positive photoresist layer on the substrate one by one; exposing one side of the substrate facing the gate for removing the second positive photoresist layer disposed right above the gate; removing the buffer layer disposed right above the gate, and preserving the buffer layer on the substrate without being covered by the gate.
 10. The method of claim 6, wherein a step of exposing one side of the substrate on the opposite side of the gate for forming a polycrystalline silicon layer comprises: exposing one side of the substrate on the opposite of the gate for only preserving the first positive photoresist layer disposed on a first section disposed right above the gate; injecting first impurity ions into the semiconductor layer outside the first section; exposing one side of the substrate on the opposite side of the gate for forming the first positive photoresist layer disposed on a second section disposed right above the gate, and the second section being smaller than the first section; injecting second impurity ions into the semiconductor layer outside the second section; removing the first positive photoresist layer disposed on the second section.
 11. The method of claim 10, wherein after removing the first positive photoresist layer on the second section, the method further comprises: coating a photoresist layer on the polycrystalline silicon layer and exposing the photoresist layer based on a desired pattern; etching the polycrystalline silicon layer without the desired pattern; removing the remaining photoresist layer.
 12. The method of claim 10, wherein the first impurity ions are N+ type impurity ions, and the second impurity ions are N− type impurity ions.
 13. The method of claim 6, wherein steps of exposing one side of the substrate on the opposite side of the gate for forming the polycrystalline silicon layer comprise: exposing one side of the substrate on the opposite side of the gate for only preserving the first positive photoresist layer disposed on a first section disposed right above the gate; injecting P-type impurity ions into the semiconductor layer outside the first section; exposing one side of the substrate on the opposite side of the gate for forming the first positive photoresist layer disposed on a second section disposed right above the gate, and the second section being smaller than the first section; removing the first positive photoresist layer disposed on the second section.
 14. A low temperature poly-silicon (LTPS) array substrate, comprising: a substrate; a gate, disposed on the substrate; forming an insulating layer and a polycrystalline silicon layer on the substrate one by one in which an upper surface of the insulating layer is a plane; a source and a drain, disposed on the polycrystalline silicon layer a pixel electrode, disposed on the insulating layer and part of the source; a plain passivation layer, disposed on a source-drain electrode layer fabricated from the source and the drain, and a contact via formed in the plain passivation layer for exposing surfaces of the gate, the source, and the drain, the contact via disposed outside the polycrystalline silicon layer; a transparent electrode layer, disposed on the plain passivation layer, and the transparent electrode layer being electrically connected to the gate, the source, and the drain via the contact hole.
 15. The LTPS array substrate of claim 14, wherein the LTPS array substrate further comprises a buffer layer, the buffer layer is disposed on the substrate without being covered by the gate, and an upper surface of the buffer layer and an upper surface of the gate form a plane. 